Android Image单指滑动双指缩放功能的最优写法

实现Android上的图片单指滑动和双指缩放功能，可以使用GestureDetector和ScaleGestureDetector两个类。具体步骤如下：

1. 在布局文件中添加一个ImageView，用于显示图片。

2. 在Activity中实例化GestureDetector和ScaleGestureDetector，并重写相应的回调方法。

public class MainActivity extends AppCompatActivity implements
        GestureDetector.OnGestureListener, GestureDetector.OnDoubleTapListener,
        ScaleGestureDetector.OnScaleGestureListener {

    private ImageView imageView;
    private GestureDetector gestureDetector;
    private ScaleGestureDetector scaleGestureDetector;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        imageView = findViewById(R.id.imageView);

        gestureDetector = new GestureDetector(this, this);
        gestureDetector.setOnDoubleTapListener(this);

        scaleGestureDetector = new ScaleGestureDetector(this, this);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        gestureDetector.onTouchEvent(event);
        scaleGestureDetector.onTouchEvent(event);
        return true;
    }

    @Override
    public boolean onDown(MotionEvent e) {
        return true;
    }

    @Override
    public void onShowPress(MotionEvent e) {

    }

    @Override
    public boolean onSingleTapUp(MotionEvent e) {
        return true;
    }

    @Override
    public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
        // 单指滑动
        if (e2.getPointerCount() == 1) {
            float dx = e2.getX() - e1.getX();
            float dy = e2.getY() - e1.getY();
            imageView.scrollBy((int) dx, (int) dy);
            return true;
        }
        return false;
    }

    @Override
    public void onLongPress(MotionEvent e) {

    }

    @Override
    public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
        return true;
    }

    @Override
    public boolean onSingleTapConfirmed(MotionEvent e) {
        return true;
    }

    @Override
    public boolean onDoubleTap(MotionEvent e) {
        // 双击缩放
        float scale = imageView.getScaleX();
        if (scale == 1.0f) {
            imageView.setScaleX(2.0f);
            imageView.setScaleY(2.0f);
        } else {
            imageView.setScaleX(1.0f);
            imageView.setScaleY(1.0f);
        }
        return true;
    }

    @Override
    public boolean onDoubleTapEvent(MotionEvent e) {
        return true;
    }

    @Override
    public boolean onScale(ScaleGestureDetector detector) {
        // 双指缩放
        float scaleFactor = detector.getScaleFactor();
        float scale = imageView.getScaleX();
        if (scaleFactor * scale >= 1.0f && scaleFactor * scale <= 3.0f) {
            imageView.setScaleX(scaleFactor * scale);
            imageView.setScaleY(scaleFactor * scale);
        }
        return true;
    }

    @Override
    public boolean onScaleBegin(ScaleGestureDetector detector) {
        return true;
    }

    @Override
    public void onScaleEnd(ScaleGestureDetector detector) {

    }
}

3. 在onTouchEvent方法中分别调用GestureDetector和ScaleGestureDetector的onTouchEvent方法。

4. 在重写的onScroll方法中，通过判断触摸点的数量来实现单指滑动。

5. 在重写的onDoubleTap方法中，通过判断当前的缩放比例来实现双击缩放。

6. 在重写的onScale方法中，通过ScaleGestureDetector获取缩放比例来实现双指缩放。

以上就是Android上实现图片单指滑动和双指缩放功能的最优写法。